1. Field of the Invention
The present invention relates to a black matrix, a phosphor screen, and a method of manufacturing thereof, and more particularly to developing the black matrix formed on the inner surface of a panel of a color cathod-ray-tube (CRT) by a wet electrophotographic method, using graphite for a main component of the black matrix materials, and forming a phosphor screen by a dry electrophotographic method to improve the quality of a color cathode-ray-tube (CRT).
2. Description of the Related Art
In a conventional shadow-mask-type CRT, graphic images are reproduced by red, green, and blue electron beams emitted from means for producing them which pass through a hole of a shadow mask, converge into a point, and collide with red, green, and blue phosphors formed on a phosphor screen of an inner surface of a panel.
The phosphor screen comprises red, green, and blue phosphors which have a pattern and black matrix which is formed on the same surface and between the phosphors. Generally, the black matrix is a photo-absorptive layer produced by using photoresisting effect of a photoresist.
The black matrix for a color CRT is produced by packing illuminescent absorptive materials between phosphors. The black matrix prevents the contrast of the CRT from decreasing, which is caused by luminescence of aluminium layer occurring when the electrons scattered around the inner panel of the CRT and the hole of a shadow mask collide with the phosphor screen. The black matrix also prevents the chromaticity from decreasing, which is caused by luminescence of dots and stripes of the phosphors when the neighboring dots and stripes are radiated by the electron beams.
In general, a process of using a photoresist for forming a black matrix takes the following steps.
A photoresist is coated on the inner surface of a panel, dried by heat or other means, and exposed by irradiation of ultraviolet rays through mask slots. The exposed panel is washed and developed to remove the unexposed photoresist and then dried. Black matrix materials are coated on the panel on which the photoresist-coated portion and photoresist-uncoated portion are regularly arranged. Then, the black matrix is produced by etching the panel. This process, however, has problems of complexity and much expenditures.
To solve the above problems, U.S. Pat. No. 4,921,767 discloses a method of manufacturing a black matrix and a phosphor screen by adjusting an electrophotographic method to reduce the number of steps in the process. A conventional process for manufacturing a black matrix and a phosphor screen for a color CRT by a dry electrophotographic method is described in FIG. 1 as follows.
A conductive layer and a photoconductive layer are coated on a washed panel, and then an electrical charge is established on the panel. The charged panel is exposed and developed by a dry electrophotographic method. A black matrix is fixed by irradiating infrared rays from an IR lamp on the panel. Electrostatically charged red, green, and blue phosphors are fixed on the panel on which the black matrix is not formed by a dry electrophotographic method.
According to the disclosure, the black matrix is mainly composed of carbon black and contains proper pigments, such as Fe--Mn oxide, etc., a polymer, and a charge control agent as subsidiary components. The mixture is dissolved by heat and mixed. The size of the mixture is about 5 .mu.m.
However, the size of the carbon black used in the disclosure is so large that the boundary of the pattern of the black matrix is not properly formed. The large size of the carbon black also causes a problem of micro-particle scattering around the pattern. Moreover, it is difficult to form a thin and dense layer on the inner surface of the panel because the carbon black used in the disclosure has a disordered hexagonal layer structure.